ICN Research Group H. Asaeda
Internet-Draft X. Shao
Intended status: Experimental NICT
Expires: January 4, 2018 T. Turletti
Inria
July 3, 2017
Contrace: Traceroute Facility for Content-Centric Network
draft-asaeda-icnrg-contrace-03
Abstract
This document describes the traceroute facility for Content-Centric
Network (CCN), named "Contrace". Contrace investigates: 1) the
routing path information per name prefix, device name, and function/
application, 2) the Round-Trip Time (RTT) between content forwarder
and consumer, and 3) the states of in-network cache per name prefix.
In addition, it discovers a gateway that supports different protocols
such as CCN and NDN.
Status of This Memo
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provisions of BCP 78 and BCP 79.
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This Internet-Draft will expire on January 4, 2018.
Copyright Notice
Copyright (c) 2017 IETF Trust and the persons identified as the
document authors. All rights reserved.
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to this document. Code Components extracted from this document must
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 6
2.1. Definitions . . . . . . . . . . . . . . . . . . . . . . . 6
3. Contrace Message Formats . . . . . . . . . . . . . . . . . . 7
3.1. Request Message . . . . . . . . . . . . . . . . . . . . . 8
3.1.1. Request Block . . . . . . . . . . . . . . . . . . . . 10
3.1.2. Report Block . . . . . . . . . . . . . . . . . . . . 13
3.2. Reply Message . . . . . . . . . . . . . . . . . . . . . . 14
3.2.1. Reply Block . . . . . . . . . . . . . . . . . . . . . 16
3.2.1.1. Reply Sub-Block . . . . . . . . . . . . . . . . . 16
4. Contrace User Behavior . . . . . . . . . . . . . . . . . . . 19
4.1. Sending Contrace Request . . . . . . . . . . . . . . . . 19
4.1.1. Gateway Discovery . . . . . . . . . . . . . . . . . . 19
4.1.2. Routing Path Information . . . . . . . . . . . . . . 20
4.1.3. In-Network Cache Information . . . . . . . . . . . . 20
4.2. Receiving Contrace Reply . . . . . . . . . . . . . . . . 20
5. Router Behavior . . . . . . . . . . . . . . . . . . . . . . . 21
5.1. Receiving Contrace Request . . . . . . . . . . . . . . . 21
5.1.1. Request Packet Verification . . . . . . . . . . . . . 21
5.1.2. Request Normal Processing . . . . . . . . . . . . . . 21
5.2. Forwarding Contrace Request . . . . . . . . . . . . . . . 22
5.3. Sending Contrace Reply . . . . . . . . . . . . . . . . . 23
5.4. Forwarding Contrace Reply . . . . . . . . . . . . . . . . 24
6. Publisher Behavior . . . . . . . . . . . . . . . . . . . . . 24
7. Contrace Termination . . . . . . . . . . . . . . . . . . . . 25
7.1. Arriving at Publisher or Gateway . . . . . . . . . . . . 25
7.2. Arriving at Router Having Cache . . . . . . . . . . . . . 25
7.3. No Route . . . . . . . . . . . . . . . . . . . . . . . . 25
7.4. No Information . . . . . . . . . . . . . . . . . . . . . 25
7.5. No Space . . . . . . . . . . . . . . . . . . . . . . . . 25
7.6. Fatal Error . . . . . . . . . . . . . . . . . . . . . . . 25
7.7. Contrace Reply Timeout . . . . . . . . . . . . . . . . . 26
7.8. Non-Supported Node . . . . . . . . . . . . . . . . . . . 26
7.9. Administratively Prohibited . . . . . . . . . . . . . . . 26
8. Configurations . . . . . . . . . . . . . . . . . . . . . . . 26
8.1. Contrace Reply Timeout . . . . . . . . . . . . . . . . . 26
8.2. HopLimit in Fixed Header . . . . . . . . . . . . . . . . 26
8.3. Access Control . . . . . . . . . . . . . . . . . . . . . 26
9. Diagnosis and Analysis . . . . . . . . . . . . . . . . . . . 27
9.1. Number of Hops . . . . . . . . . . . . . . . . . . . . . 27
9.2. Caching Router and Gateway Identification . . . . . . . . 27
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9.3. TTL or Hop Limit . . . . . . . . . . . . . . . . . . . . 27
9.4. Time Delay . . . . . . . . . . . . . . . . . . . . . . . 27
9.5. Path Stretch . . . . . . . . . . . . . . . . . . . . . . 27
9.6. Cache Hit Probability . . . . . . . . . . . . . . . . . . 27
10. Security Considerations . . . . . . . . . . . . . . . . . . . 28
10.1. Policy-Based Information Provisioning for Request . . . 28
10.2. Filtering of Contrace Users Located in Invalid Networks 28
10.3. Topology Discovery . . . . . . . . . . . . . . . . . . . 29
10.4. Characteristics of Content . . . . . . . . . . . . . . . 29
10.5. Longer or Shorter Contrace Reply Timeout . . . . . . . . 29
10.6. Limiting Request Rates . . . . . . . . . . . . . . . . . 29
10.7. Limiting Reply Rates . . . . . . . . . . . . . . . . . . 29
10.8. Adjacency Verification . . . . . . . . . . . . . . . . . 30
11. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 30
12. References . . . . . . . . . . . . . . . . . . . . . . . . . 30
12.1. Normative References . . . . . . . . . . . . . . . . . . 30
12.2. Informative References . . . . . . . . . . . . . . . . . 30
Appendix A. Contrace Command and Options . . . . . . . . . . . . 31
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 33
1. Introduction
In Content-Centric Network (CCN) or Named-Data Network (NDN),
publishers provide content through the network, and receivers
retrieve content by name. In this network architecture, routers
forward content requests by means of their Forwarding Information
Bases (FIBs), which are populated by name-based routing protocols.
CCN/NDN also enables receivers to retrieve content from an in-network
cache.
In CCN/NDN, while consumers do not generally need to know which
content forwarder is transmitting the content to them, operators and
developers may want to identify the content forwarder and observe the
routing path information per name prefix for troubleshooting or
investigating the network conditions.
Traceroute [5] is a useful tool for analyzing the routing conditions
in IP networks as it provides intermediate router addresses along the
path between source and destination and the Round-Trip Time (RTT) for
the path. However, this IP-based network tool cannot trace the name
prefix paths used in CCN/NDN. Moreover, given a source-rooted
routing path per name prefix, specifying a forwarding source (i.e.,
router or publisher) for any content is difficult, because we do not
always know which branch of the source tree the consumer is on.
Additionally, it is not feasible to flood the entire source-rooted
tree to find the path from a source to a consumer. Furthermore, such
IP-based network tool does not allow the states of the in-network
cache to be discovered.
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This document describes the specification of "Contrace", an active
network measurement tool for investigating the path and caching
condition in CCN. Contrace potentially discovers devices and
functions/applications in CCN. Contrace is designed based on the
work originally published in [4].
Contrace consists of the Contrace user command and the Contrace
forwarding function implementation on a content forwarder (e.g.,
router). The Contrace user (e.g., consumer) invokes the contrace
command (described in Appendix A) with the name prefix of the
content, the device name, or the function (or application) name. The
Contrace command initiates the Contrace "Request" message (described
in Section 3.1). The Request message, for example, obtains routing
path and cache information. When an appropriate adjacent neighbor
router receives the Request message, it retrieves cache information.
If the router is not the content forwarder for the request, it
inserts its "Report" block (described in Section 3.1.2) into the
Request message and forwards the Request message to its upstream
neighbor router(s) decided by its FIB. These two message types,
Contrace Request and Reply messages, are encoded in the CCNx TLV
format [1].
In this way, the Contrace Request message is forwarded by routers
toward the content publisher, and the Contrace Report record is
inserted by each intermediate router. When the Request message
reaches the content forwarder (i.e., a router or the publisher who
has the specified cache or content), the content forwarder forms the
Contrace "Reply" message (described in Section 3.2) and sends it to
the downstream neighbor router. The Reply message is forwarded back
toward the Contrace user in a hop-by-hop manner. This request-reply
message flow, walking up the tree from a consumer toward a publisher,
is inspired by the design of the IP multicast traceroute facility
[6].
Contrace supports multipath forwarding. The Request messages can be
forwarded to multiple neighbor routers. When the Request messages
forwarded to multiple routers, the different Reply messages will be
forwarded from different routers or publisher. To support this case,
PIT entries initiated by Contrace remain until the defined timeout
value is expired.
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1. Request 2. Request 3. Request 4. Request
(+U) (U+A) (U+A+B) (U+A+B+C)
+----+ +----+ +----+ +----+
| | | | | | | |
| v | v | v | v
+--------+ +--------+ +--------+ +--------+ +---------+
|Contrace|----| Router |----| Router |----| Router |----|Publisher|
| user | | A | | B | | C | | |
+--------+ +--------+ +--------+ +--------+ +---------+
\
\ +-------+
3. Request \ | Cache |
(U+A+B) \ +---------+ |
v| Caching |----+
| router |
+---------+
Figure 1: Request messages forwarded by consumer and routers.
Contrace user and routers (i.e., Router A,B,C) insert their own
Report blocks into the Request message and forward the message toward
the content forwarder (i.e., caching router and publisher)
3. Reply(C) 2. Reply(C)
4. Reply(P) 3. Reply(P) 2. Reply(P) 1. Reply(P)
+----+ +----+ +----+ +----+
| | | | | | | |
v | v | v | v |
+--------+ +--------+ +--------+ +--------+ +---------+
|Contrace|----| Router |----| Router |----| Router |----|Publisher|
| user | | A | | B | | C | | |
+--------+ +--------+ +--------+ +--------+ +---------+
^
\ +-------+
1. Reply(C) \ | Cache |
\ +---------+ |
\| Caching |----+
| router |
+---------+
Figure 2: Reply messages forwarded by publisher and routers. Each
router forwards the Reply message, and finally the Contrace user
receives two Reply messages: one from the publisher and the other
from the caching router.
Contrace facilitates the tracing of a routing path and provides: 1)
the RTT between content forwarder (i.e., caching router or publisher)
and consumer, 2) the states of in-network cache per name prefix, and
3) the routing path information per name prefix.
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In addition, Contrace identifies the states of the cache, such as the
following metrics for Content Store (CS) in the content forwarder: 1)
size of the cached content, 2) number of the cached chunks of the
content, 3) number of the accesses (i.e., received Interests) per
cache or chunk, and 4) lifetime and expiration time per cache or
chunk. The number of received Interests per cache or chunk on the
routers indicates the popularity of the content.
Furthermore, Contrace implements policy-based information
provisioning that enables administrators to "hide" secure or private
information, but does not disrupt the forwarding of messages. This
policy-based information provisioning reduces the deployment barrier
faced by operators in installing and running Contrace on their
routers.
2. Terminology
In this document, the key words "MUST", "MUST NOT", "REQUIRED",
"SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY",
and "OPTIONAL" are to be interpreted as described in RFC 2119 [2],
and indicate requirement levels for compliant Contrace
implementations.
2.1. Definitions
Since Contrace requests flow in the opposite direction to the data
flow, we refer to "upstream" and "downstream" with respect to data,
unless explicitly specified.
Router
It is a router facilitating name-based content/device/function
name or characteristic retrieval in the path between consumer and
publisher.
Scheme name
It indicates a URI and protocol such as "ccnx:/" and "ndn:/".
This document considers the protocol for name-based
content/device/function name or characteristic retrieval.
Gateway
It is a router supporting multiple scheme names in the path
between consumer and publisher. The router has multiple FIBs for
different protocols and establishes the connections with different
neighbor routers for each protocol.
Node
It is a router, gateway, publisher, or consumer.
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Content forwarder
It is either a caching router or a publisher that holds the cache
(or content) and forwards it to consumers.
Contrace user
It is a node that invokes the contrace command and initiates the
Contrace Request.
Incoming face
The face on which data is expected to arrive from the specified
name prefix.
Outgoing face
The face to which data from the publisher or router is expected to
transmit for the specified name prefix. It is also the face on
which the Contrace Request messages are received.
3. Contrace Message Formats
Contrace uses two message types: Request and Reply. Both messages
are encoded in the CCNx TLV format ([1], Figure 3). The Request
message consists of a fixed header, Request block TLV Figure 7, and
Report block TLV(s) Figure 11. The Reply message consists of a fixed
header, Request block TLV, Report block TLV(s), and Reply block/sub-
block TLV(s) Figure 14.
1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+---------------+---------------+---------------+---------------+
| Version | PacketType | PacketLength |
+---------------+---------------+---------------+---------------+
| PacketType specific fields | HeaderLength |
+---------------+---------------+---------------+---------------+
/ Optional Hop-by-hop header TLVs /
+---------------+---------------+---------------+---------------+
/ PacketPayload TLVs /
+---------------+---------------+---------------+---------------+
/ Optional CCNx ValidationAlgorithm TLV /
+---------------+---------------+---------------+---------------+
/ Optional CCNx ValidationPayload TLV (ValidationAlg required) /
+---------------+---------------+---------------+---------------+
Figure 3: Packet format [1]
The Request and Reply Type values in the fixed header are
PT_PING_TRACE_REQ and PT_PING_TRACE_REPLY, respectively (Figure 4).
These messages are forwarded in a hop-by-hop manner. When the
Request message reaches the content forwarder, the content forwarder
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turns the Request message into a Reply message by changing the Type
field value in the fixed header from PT_PING_TRACE_REQ to
PT_PING_TRACE_REPLY and forwards back to the node that has initiated
the Request message.
Code Type name
======== =====================
1 PT_INTEREST [1]
2 PT_CONTENT [1]
3 PT_RETURN [1]
4 PT_PING_TRACE_REQ
5 PT_PING_TRACE_REPLY
Figure 4: Packet Type Namespace
Each Contrace message MUST begin with a fixed header with either a
Request or Reply type value to specify whether it is a Request
message or Reply message. Following a fixed header, there can be a
sequence of optional hop-by-hop header TLV(s) for a Request message.
In the case of a Request message, it is followed by a sequence of
Report blocks, each from a router on the path toward the publisher or
caching router.
At the beginning of PacketPayload TLVs, one top-level TLV type,
T_TRACE (Figure 5), exists at the outermost level of a CCNx protocol
message. This TLV indicates that the Name segment TLV(s) and Reply
block TLV(s) would follow in the Request or Reply message.
Code Type name
======== =========================
1 T_INTEREST [1]
2 T_OBJECT [1]
3 T_VALIDATION_ALG [1]
4 T_VALIDATION_PAYLOAD [1]
5 T_PING
6 T_TRACE
Figure 5: Top-Level Type Namespace
3.1. Request Message
When a Contrace user initiates a trace request (e.g., by contrace
command described in Appendix A), a Contrace Request message is
created and forwarded to its upstream router through the Incoming
face(s) determined by its FIB.
The Contrace Request message format is as shown in Figure 6. It
consists of a fixed header, Request block TLV (Figure 7), Report
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block TLV(s) (Figure 11), and Name TLV. The Type value of Top-Level
type namespace is T_TRACE (Figure 5). The Type value for the Report
message is PT_PING_TRACE_REQ.
1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+---------------+---------------+---------------+---------------+
| Version | PacketType | PacketLength |
+---------------+---------------+---------------+---------------+
| HopLimit | ReturnCode |Reserved (MBZ) | HeaderLength |
+===============+===============+===============+===============+
| |
+ Request block TLV +
| |
+---------------+---------------+---------------+---------------+
/ Report block TLV 1 /
+---------------+---------------+---------------+---------------+
/ Report block TLV 2 /
+---------------+---------------+---------------+---------------+
/ . /
/ . /
+---------------+---------------+---------------+---------------+
/ Report block TLV n /
+===============+===============+===============+===============+
| T_TRACE | MessageLength |
+---------------+---------------+---------------+---------------+
| T_NAME | Length |
+---------------+---------------+---------------+---------------+
/ Name segment TLVs (name prefix specified by contrace command) /
+---------------+---------------+---------------+---------------+
Figure 6: Request message consists of a fixed header, Request block
TLV, Report block TLV(s), and Name TLV
HopLimit: 8 bits
HopLimit is a counter that is decremented with each hop. It
limits the distance a Request may travel on the network.
ReturnCode: 8 bits
ReturnCode is used for the Reply message. This value is replaced
by the content forwarder when the Request message is returned as
the Reply message (see Section 3.2). Until then, this field MUST
be transmitted as zeros and ignored on receipt.
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Value Name Description
----- --------------- ----------------------------------------------
0x00 NO_ERROR No error
0x01 WRONG_IF Contrace Request arrived on an interface
to which this router would not forward for
the specified name/function toward the
publisher.
0x02 INVALID_REQUEST Invalid Contrace Request is received.
0x03 NO_ROUTE This router has no route for the name prefix
and no way to determine a potential route.
0x04 NO_INFO This router has no cache information for the
specified name prefix, device information, or
function.
0x05 NO_SPACE There was not enough room to insert another
Report block in the packet.
0x06 NO_GATAWAY Contrace Request arrived on a non-gateway
router.
0x07 INFO_HIDDEN Information is hidden from this trace because
of some policy.
0x0E ADMIN_PROHIB Contrace Request is administratively
prohibited.
0x0F UNKNOWN_REQUEST This router does not support/recognize the
Request message.
0x80 FATAL_ERROR A fatal error is one where the router may
know the upstream router but cannot forward
the message to it.
Reserved (MBZ): 8 bits
The reserved fields in the Value field MUST be transmitted as
zeros and ignored on receipt.
3.1.1. Request Block
When a Contrace user transmits the Request message, it MUST insert
the Request block TLV (Figure 7) and the Report block TLV (Figure 11)
of its own to the Request message before sending it through the
Incoming face(s).
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1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+---------------+---------------+---------------+---------------+
| T_TRACE_REQ | Length |
+---------------+---------------+-----+-------------------------+
| SchemeName | SkipHopCount |TimeO| Reserved (MBZ) |
+---------------+---------------+-----+-------------------------+
| Request ID | Flags |
+---------------+---------------+-------------------------------+
Figure 7: Request block TLV (hop-by-hop header)
Code Type name
============= =====================
1 T_INTLIFE [1]
2 T_CACHETIME [1]
3 T_MSGHASH [1]
4 - 7 Reserved [1]
8 T_TRACE_REQ
9 T_TRACE_REPORT
%x0FFE T_PAD [1]
%x0FFF T_ORG [1]
%x1000-%x1FFF Reserved [1]
Figure 8: Hop-by-Hop Type Namespace
Type: 16 bits
Format of the Value field. For the single Request block TLV, the
type value MUST be T_TRACE_REQ. For all the available types for
hop-by-hop type namespace, please see Figure 8.
Length: 16 bits
Length of Value field in octets. For the Request block, it MUST
be 4 in the current specification.
SchemeName: 8 bits
Currently, the following scheme names are defined.
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Code Scheme name
============= ===============
0 ccnx:/
1 ndn:/
2 cefore:/
%x03-%FF Not assigned
Figure 9: Scheme Names
SkipHopCount: 8 bits
Number of skipped routers. This value MUST be lower than the
value of HopLimit at the fixed header.
TimeO: 3 bits
Timeout value (seconds). This Timeout value means a [Contrace
Reply Timeout] value (seconds) requested by the Contrace user
later described in Section 8.1. A Contrace user requests routers
along the path to keep the PIT entry for the Request until this
timeout value expires. Note that, because of some security
concern (Section 10.5), a router along the path may configure the
shorter timeout value than this requested timeout value. In that
case, the Request may be timed out and the Contrace user may not
receive the Reply as expected.
Request ID: 16 bits
This field is used as a unique identifier for this Contrace
Request so that duplicate or delayed Reply messages can be
detected.
Flags: 16 bits
The trace conditions specified as the contrace command options
(described in Appendix A) are transferred in the Flags field. The
trace conditions depend on the specified name (i.e., name_prefix,
device_name, or function_name) as shown in Figure 10. Note that
code %x01 and %x02 are exclusive options; that is, only one of
them should be turned on at once.
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Code Type name
============ =====================================================
%x01 Cache retrieval allowing partial match (name_prefix)
%x02 No cache information required (name_prefix)
%x04 Publisher reachability (name_prefix and device_name)
%x08 Force trace. Request to multiple upstream routers
simultaneously (name_prefix, device_name, and
function_name)
%x16 Discovery of gateway supporting specified scheme
name (name_prefix, device_name, and function_name)
%x32 Function's or application's version number retrieval
(function_name)
%x64-%x32768 Not assigned
Figure 10: Codes and types specified in Flags field
3.1.2. Report Block
A Contrace user and each upstream router along the path would insert
its own Report block TLV without changing the Type field of the fixed
header of the Request message until one of these routers is ready to
send a Reply. In the Report block TLV (Figure 11), the Request
Arrival Time and the Node Identifier MUST be inserted.
1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+---------------+---------------+---------------+---------------+
| T_TRACE_REPORT | Length |
+---------------+---------------+---------------+---------------+
| Request Arrival Time |
+---------------+---------------+---------------+---------------+
/ Node Identifier /
+---------------+---------------+---------------+---------------+
Figure 11: Report block TLV (hop-by-hop header)
Type: 16 bits
Format of the Value field. For the Request block TLV(s), the type
value(s) MUST be T_TRACE_REPORT.
Length: 16 bits
Length of Value field in octets.
Request Arrival Time: 32 bits
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The Request Arrival Time is a 32-bit NTP timestamp specifying the
arrival time of the Contrace Request packet at this router. The
32-bit form of an NTP timestamp consists of the middle 32 bits of
the full 64-bit form; that is, the low 16 bits of the integer part
and the high 16 bits of the fractional part.
The following formula converts from a UNIX timeval to a 32-bit NTP
timestamp:
request_arrival_time
= ((tv.tv_sec + 32384) << 16) + ((tv.tv_nsec << 7) / 1953125)
The constant 32384 is the number of seconds from Jan 1, 1900 to
Jan 1, 1970 truncated to 16 bits. ((tv.tv_nsec << 7) / 1953125)
is a reduction of ((tv.tv_nsec / 1000000000) << 16).
Note that Contrace does not require all the routers on the path to
have synchronized clocks in order to measure one-way latency.
Node Identifier: variable length
This field specifies the Contrace user or the router identifier
(e.g., IPv4 address) of the Incoming face on which packets from
the publisher are expected to arrive, or all-zeros if unknown or
unnumbered. Since we may not always rely on the IP addressing
architecture, it would be necessary to define the identifier
uniqueness (e.g., by specifying the protocol family) for this
field. However, defining such uniqueness is out of scope of this
document. Potentially, this field may be defined as a new TLV,
which might be defined in the document for the CCNx TLV format[1].
3.2. Reply Message
When a content forwarder receives a Contrace Request message from the
appropriate adjacent neighbor router, it would insert a Reply block
TLV and Reply sub-block TLV(s) of its own to the Request message and
turn the Request into the Reply by changing the Type field of the
fixed header of the Request message from PT_PING_TRACE_REQ to
PT_PING_TRACE_REPLY. The Reply message (see Figure 12) would then be
forwarded back toward the Contrace user in a hop-by-hop manner.
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1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+---------------+---------------+---------------+---------------+
| Version | PacketType | PacketLength |
+---------------+---------------+---------------+---------------+
| HopLimit | ReturnCode |Reserved (MBZ) | HeaderLength |
+===============+===============+===============+===============+
| |
+ Request block TLV +
| |
+---------------+---------------+---------------+---------------+
/ . /
/ . /
/ n Report block TLVs /
/ . /
/ . /
+===============+===============+===============+===============+
| T_TRACE | MessageLength |
+---------------+---------------+---------------+---------------+
| T_NAME | Length |
+---------------+---------------+---------------+---------------+
/ Name segment TLVs (name prefix specified by contrace command) /
+---------------+---------------+---------------+---------------+
/ Reply block TLV /
+---------------+---------------+---------------+---------------+
/ Reply sub-block TLV 1 /
+---------------+---------------+---------------+---------------+
/ Reply sub-block TLV 2 /
+---------------+---------------+---------------+---------------+
/ . /
/ . /
+---------------+---------------+---------------+---------------+
/ Reply sub-block TLV k /
+---------------+---------------+---------------+---------------+
Figure 12: Reply message consists of a fixed header, Request block
TLV, Report block TLV(s), Name TLV, and Reply block/sub-block TLV(s)
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Code Type name
============= =====================
0 T_NAME [1]
1 T_PAYLOAD [1]
2 T_KEYIDRESTR [1]
3 T_OBJHASHRESTR [1]
5 T_PAYLDTYPE [1]
6 T_EXPIRY [1]
8 T_TRACE_REPLY
9 - 12 Reserved [1]
%x0FFE T_PAD [1]
%x0FFF T_ORG [1]
%x1000-%x1FFF Reserved [1]
Figure 13: CCNx Message Type Namespace
3.2.1. Reply Block
The Reply block TLV is an envelope for Reply sub-block TLV(s)
(explained in Section 3.2.1.1).
1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+---------------+---------------+---------------+---------------+
| T_TRACE_REPLY | Length |
+---------------+---------------+---------------+---------------+
Figure 14: Reply block TLV (packet payload)
Type: 16 bits
Format of the Value field. For the Report block TLV, the type
value MUST be T_TRACE_REPLY.
Length: 16 bits
Length of Value field in octets. This length is a total length of
Reply sub-block(s).
3.2.1.1. Reply Sub-Block
In addition to the Reply block, a router on the traced path will add
one or multiple Reply sub-blocks followed by the Reply block before
sending the Reply to its neighbor router.
The Reply sub-block is flexible for various purposes. For instance,
operators and developers may want to obtain various characteristics
of content such as content's ownership and copyright, or other cache
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states and conditions. Various information about device or function
(or application) may be also retrieved by the variety of Reply sub-
blocks. In this document, Reply sub-block TLVs for T_TRACE_CONTENT
and T_TRACE_CONTENT_OWNER (Figure 15) and for T_TRACE_GATEWAY
(Figure 16) are defined; other Reply sub-block TLVs will be defined
in separate document(s).
1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+---------------+---------------+---------------+---------------+
| Type | Length |
+---------------+---------------+---------------+---------------+
| Content Size |
+---------------+---------------+---------------+---------------+
| Object Count |
+---------------+---------------+---------------+---------------+
| # Received Interest |
+---------------+---------------+---------------+---------------+
| First Seqnum |
+---------------+---------------+---------------+---------------+
| Last Seqnum |
+---------------+---------------+---------------+---------------+
| Cache Lifetime |
+---------------+---------------+---------------+---------------+
| Remain Cache Lifetime |
+---------------+---------------+---------------+---------------+
| T_NAME | Length |
+---------------+---------------+---------------+---------------+
/ Name segment TLVs (name prefix partially/exactly matched) /
+---------------+---------------+---------------+---------------+
Figure 15: Reply sub-block TLV for T_TRACE_CONTENT and
T_TRACE_CONTENT_OWNER (packet payload)
1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+---------------+---------------+---------------+---------------+
| Type | Length |
+---------------+---------------+---------------+---------------+
| Scheme Name | Reserved (MBZ) |
+---------------+---------------+---------------+---------------+
Figure 16: Reply sub-block TLV for T_TRACE_GATEWAY (packet payload)
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Code Type name
============= ===========================
0 T_TRACE_CONTENT
1 T_TRACE_CONTENT_OWNER
2 T_TRACE_GATEWAY
3 T_TRACE_DEVICE
4 T_TRACE_FUNCTION
%x0FFF T_ORG
%x1000-%x1FFF Reserved (Experimental Use)
Figure 17: Contrace Reply Type Namespace
Type: 16 bits
Format of the Value field. For the Reply sub-block TLV, the type
value MUST be one of the type value defined in the Contrace Reply
Type Namespace (Figure 17). T_TRACE_CONTENT is specified when the
cache information is replied from a caching router.
T_TRACE_CONTENT_OWNER is specified when the content information is
replied from a publisher. T_TRACE_GATEWAY is used to discover a
gateway that has a FIB for the specified scheme name.
Length: 16 bits
Length of Value field in octets.
Scheme Name: 8 bits
The code of the scheme name defined in Figure 9.
Content Size: 32 bits
The total size (MB) of the (cached) content objects. Note that
the maximum size expressed by 32 bit field is 65 GB.
Object Count: 32 bits
The number of the (cached) content objects.
# Received Interest: 32 bits
The number of the received Interest messages to retrieve the
content.
First Seqnum: 32 bits
The first sequential number of the (cached) content objects.
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Last Seqnum: 32 bits
The last sequential number of the (cached) content objects. Above
First Seqnum and this Last Seqnum do not guarantee the
consecutiveness of the cached content objects.
Cache Lifetime: 32 bits
The elapsed time after the oldest content object in the cache is
stored. The Cache Lifetime is a 32-bit NTP timestamp, and the
formula converts from a UNIX timeval to a 32-bit NTP timestamp is
same as that of Section 3.1.2.
Remain Cache Lifetime: 32 bits
The lifetime of a content object, which is removed first among the
cached content objects. The Remain Cache Lifetime is a 32-bit NTP
timestamp.
4. Contrace User Behavior
4.1. Sending Contrace Request
A Contrace user initiates a Contrace Request by sending the Request
message to the adjacent neighbor router(s) of interest. As a typical
example, a Contrace user invokes the contrace command (detailed in
Appendix A) that forms a Request message and sends it to the user's
adjacent neighbor router(s).
When the Contrace user's program initiates a Request message, it MUST
insert the necessary values, the "Request ID" (in the Request block)
and the "Node Identifier" (in the Report block), in the Request and
Report blocks. Contrace user's program MUST also record the Request
ID at the corresponding PIT entry. The Request ID is a unique
identifier for the Contrace Request.
After the Contrace user's program sends the Request message, until
the Reply times out, the Contrace user's program MUST keep the
following information; Request ID and Flags specified in the Request
block, Node Identifier and Request Arrival Time specified in the
Report block, and HopLimit specified in the fixed header.
4.1.1. Gateway Discovery
A Contrace Request can be used for gateway discovery; if a Contrace
user invokes a Contrace Request with a scheme name (e.g., ccnx:/ or
ndn:/) and the "gateway discovery" flag value (i.e., "%x16" bit as
seen in Figure 10), s/he could potentially discover a gateway that
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supports different protocols such as CCN and NDN. The Contrace
Request for gateway discovery only indicates the routing path
information (see Section 4.1.2) and the scheme name whether the
router is a gateway or not; it does not provide other information,
e.g., cache information.
4.1.2. Routing Path Information
A Contrace user can send a Contrace Request for investigating routing
path information for the specified named content. By the Request,
the legitimate user can obtain; 1) identifiers (e.g., IP addresses)
of intermediate routers, 2) identifier of content forwarder, 3)
number of hops between content forwarder and consumer, and 4) RTT
between content forwarder and consumer, per name prefix. This
Contrace Request is terminated when it reaches the content forwarder.
The contrace command enables user to obtain both the routing path
information and in-network cache information (see below) in a same
time.
4.1.3. In-Network Cache Information
A Contrace user can send a Contrace Request for investigating in-
network cache information. By this Request, the legitimate user can
obtain; 1) size of the cached content, 2) number of the cached chunks
of the content, 3) number of the accesses (i.e., received Interests)
per cache or chunk, and 4) lifetime and expiration time per cache or
chunk, for Content Store (CS) in the content forwarder. This
Contrace Request is terminated when it reaches the content forwarder.
4.2. Receiving Contrace Reply
A Contrace user's program will receive one or multiple Contrace Reply
messages from the adjacent neighbor router that has previously
received and forwarded the Request message(s). When the program
receives the Reply, it MUST compare the kept Request ID and the
Request ID noted in the Reply. If they do not match, the Reply
message SHOULD be silently discarded.
If the number of the Report blocks in the received Reply is more than
the initial HopLimit value (which was inserted in the original
Request) + 1, the Reply SHOULD be silently ignored.
After the Contrace user has determined that s/he has traced the whole
path or as much as s/he can expect to, s/he might collect statistics
by waiting a timeout. Useful statistics provided by Contrace can be
seen in Section 9.
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5. Router Behavior
5.1. Receiving Contrace Request
5.1.1. Request Packet Verification
Upon receiving a Contrace Request message, a router MUST examine
whether the message comes from a valid adjacent neighbor node. If it
is invalid, the Request MUST be silently ignored. The router next
examines the value of the "HopLimit" in the fixed header and the
value of the "SkipHopCount" in the Request block (Figure 7). If
SkipHopCount value is equal or more than the HopLimit value, the
Request MUST be silently ignored.
5.1.2. Request Normal Processing
When a router receives a Contrace Request message, it performs the
following steps.
1. HopLimit and SkipHopCount are counters that are decremented with
each hop. The router terminates the Contrace Request when the
HopLimit value becomes zero. Until the SkipHopCount value
becomes zero, the router forwards the Contrace Request messages
to the upstream router(s) (if it knows) without adding its own
Report block and without replying the Request. If the router
does not know the upstream router(s), without depending on the
SkipHopCount value, it replies the Contrace Reply message with
NO_ROUTE return code.
2. The router examines the Flags field of the Request block of
received Contrace Request. If the flag value indicates "%x00" or
"%x01" bit (as seen in Figure 10) for "cache information
discovery", the router examines its FIB and CS. If the router
caches the specified content, it inserts own Report block to the
message and sends the Reply message with own Reply block and sub-
block. If the router does not cache the specified content but
knows the neighbor router(s) for the specified name prefix, it
inserts own Report block and forwards the Request to the upstream
neighbor(s). If the router does not cache the specified content
and does not know the upstream neighbor router(s) for the
specified name prefix, it replies the Contrace Reply message with
NO_ROUTE return code.
3. If the flag value indicates "%x02" bit for "routing path
information discovery", the router examines its FIB and CS. If
the router caches the specified content, it inserts own Report
block to the message and sends the Reply message with own Reply
block. The router does not insert any Reply sub-block here. If
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the router does not cache the specified content but knows the
neighbor router(s) for the specified name prefix, it inserts own
Report block and forwards the Request to the upstream
neighbor(s). If the router does not cache the specified content
and does not know the upstream neighbor router(s) for the
specified name prefix, it replies the Contrace Reply message with
NO_ROUTE return code.
4. If the flag value indicates "%x04" bit for "publisher discovery",
the node receiving the Request message examines whether it owns
the requested content as the publisher. If it is the publisher,
it sends the Reply message with own Report block and sub-block.
If the node is not the publisher but know the upstream neighbor
router(s) for the specified name prefix, it adds the own Report
block and forwards the Request to the neighbor(s). If the node
is not the publisher and does not know the upstream neighbor
router(s) for the specified name prefix, it replies the Contrace
Reply message with NO_ROUTE return code.
5. When a router receives a Contrace Request in which the "gateway
discovery" flag (i.e., "%x16") is set in the Flags field and a
scheme name is specified, the router examines whether it has the
FIB for the specified scheme name and the connections with the
neighbor router(s) for the scheme protocol. If the router is the
gateway, it sends the Reply message back toward the Contrace
user. If the router does not have the FIB for the specified
scheme name or does not connect to any neighbor router for the
specified scheme name, the router returns the Reply with
NO_GATEWAY return code.
5.2. Forwarding Contrace Request
When a router decides to forward a Request message with its Report
block to its upstream router(s), it specifies the Request Arrival
Time and Node Identifier in the Report block of the Request message.
The router then forwards the Request message upstream toward the
publisher or caching router based on the FIB entry.
When the router forwards the Request message, it MUST record the
Request ID at the corresponding PIT entry. The router can later
decide the PIT entry to correctly forward back the Reply message even
if it receives multiple Reply messages within the same timeout
period. (See below.)
Contrace supports multipath forwarding. The Request messages can be
forwarded to multiple neighbor routers. Some router may have
strategy for multipath forwarding; when it sends Interest messages to
multiple neighbor routers, it may delay or prioritize to send the
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message to the upstream routers. The Contrace Request, as the
default, complies with such strategy; a Contrace user could trace the
actual forwarding path based on the strategy. On the other hand,
there may be the case that a Contrace user wants to discover all
potential forwarding paths based on routers' FIBs. If a Contrace
user invokes a Contrace Request with the force flag value (i.e.,
"%x08" bit as seen in Figure 10), the forwarding strategy will be
ignored and the router sends Requests to multiple upstream routers
simultaneously, and the Contrace user could trace the all potential
forwarding paths.
When the Request messages forwarded to multiple routers, the
different Reply messages will be forwarded from different routers or
publisher. To support this case, PIT entries initiated by Contrace
remain until the configured Contrace Reply Timeout (Section 8.1)
passes. In other words, unlike the ordinary Interest-Data
communications in CCN, the router SHOULD NOT remove the PIT entry
created by the Contrace Request before the timeout value expires,
even if the router receives the Contrace Reply.
Contrace Requests SHOULD NOT result in PIT aggregation in routers
during the Request message transmission.
5.3. Sending Contrace Reply
When a router decides to send a Reply message to its downstream
neighbor router or the Contrace user with NO_ERROR return code, it
inserts a Report block having the Request Arrival Time and Node
Identifier to the hop-by-hop TLV header of the Request message. And
then the router inserts the corresponding Reply block and Reply sub-
block to the payload. The router does not insert any Reply block/
sub-block if there is an error. The router finally changes the Type
field in the fixed header from PT_PING_TRACE_REQ to
PT_PING_TRACE_REPLY and forwards the message back as the Reply toward
the Contrace user in a hop-by-hop manner.
When a router decides to send the Reply message for the Request for
the cache or routing path information discovery, it forms the Reply
message including a Reply block and a Reply sub-block with the
T_TRACE_CONTENT type value (Figure 15) and various cache information.
After the router puts the NO_ERROR return code in the fixed header,
it sends the Reply back toward the Contrace user.
When a router decides to send the Reply message for the Request for
the publisher discovery, it forms the Reply message including a Reply
block and a Reply sub-block with the T_TRACE_CONTENT_OWNER type value
(Figure 15) and various cache information. After the router puts the
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NO_ERROR return code in the fixed header, it sends the Reply back
toward the Contrace user.
When a router decides to send the Reply message for the Request for
the gateway discovery, it forms the Reply message including a Reply
block and a Reply sub-block with the T_TRACE_GATEWAY type value
(Figure 16) and the scheme name (Figure 9). After the router puts
the NO_ERROR return code in the fixed header, it sends the Reply back
toward the Contrace user.
If a router cannot continue the Request, it MUST put an appropriate
ReturnCode in the Request message, change the Type field value in the
fixed header from PT_PING_TRACE_REQ to PT_PING_TRACE_REPLY, and
forward the Reply message back toward the Contrace user, to terminate
the request. See Section 7.
5.4. Forwarding Contrace Reply
When a router receives a Contrace Reply whose Request ID matches the
one in the original Contrace Request block TLV from a valid adjacent
neighbor node, it MUST relay the Contrace Reply back to the Contrace
user. If the router does not receive the corresponding Reply within
the [Contrace Reply Timeout] period, then it removes the
corresponding PIT entry and terminates the trace.
Contrace Replies MUST NOT be cached in routers upon the Reply message
transmission.
6. Publisher Behavior
Upon receiving a Contrace Request message, a publisher MUST examine
whether the message comes from a valid adjacent neighbor node. If it
is invalid, the Request SHOULD be silently ignored.
If a publisher cannot accept the Request, it will note an appropriate
ReturnCode in the Request message, change the Type field value in the
fixed header from PT_PING_TRACE_REQ to PT_PING_TRACE_REPLY, and
forward the message as the Reply back to the Contrace user. See
Section 7 for details.
If a publisher accepts the Request forwarded by a valid adjacent
neighbor node, it retrieves the local content information. The Reply
message having a Reply block and Reply sub-block is transmitted back
to the neighbor node that had forwarded the Request message.
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7. Contrace Termination
When performing an expanding hop-by-hop trace, it is necessary to
determine when to stop expanding. There are several cases an
intermediate router might return a Reply before a Request reaches the
caching router or the publisher.
7.1. Arriving at Publisher or Gateway
A Contrace Request can be determined to have arrived at the publisher
or gateway.
7.2. Arriving at Router Having Cache
A Contrace Request can be determined to have arrived at the router
having the specified content cache within the specified HopLimit.
7.3. No Route
If the router cannot determine the routing paths or neighbor routers
for the specified name prefix, device name, or function within the
specified HopLimit, the router MUST note a ReturnCode of NO_ROUTE in
the fixed header of the message, and forwards the message as the
Reply back to the Contrace user.
7.4. No Information
If the router does not have any information about the specified name
prefix, device name, or function within the specified HopLimit, the
router MUST note a ReturnCode of NO_INFO in the fixed header of the
message, and forwards the message as the Reply back to the Contrace
user.
7.5. No Space
If appending the Report block would make the Contrace Request packet
longer than the MTU of the Incoming face, or longer than 1280 bytes
(especially in the situation supporting IPv6 as the payload [3]), the
router MUST note a ReturnCode of NO_SPACE in the fixed header of the
message, and forwards the message as the Reply back to the Contrace
user.
7.6. Fatal Error
A Contrace Request has encountered a fatal error if the last
ReturnCode in the trace has the 0x80 bit set (see Section 3.1).
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7.7. Contrace Reply Timeout
If a Contrace user or a router encounters the Request or Reply
message whose expires its own [Contrace Reply Timeout] value
(Section 8.1), which is used to time out a Contrace Reply such as the
case of Section 7.8.
7.8. Non-Supported Node
Cases will arise in which a router or a publisher along the path does
not support Contrace. In such cases, a Contrace user and routers
that forward the Contrace Request will time out the Contrace request.
7.9. Administratively Prohibited
If Contrace is administratively prohibited, a router or a publisher
rejects the Request message, and the router or the publisher, or its
downstream router will reply the Contrace Reply with the ReturnCode
of ADMIN_PROHIB.
8. Configurations
8.1. Contrace Reply Timeout
The [Contrace Reply Timeout] value is used to time out a Contrace
Reply. Both Contrace users and routers can configure their own
Contrace Reply Timeout values. Contrace users, for example, can
configure the timeout value by the contrace command. The default
[Contrace Reply Timeout] value is 4 (seconds). Routers may want to
configure the short timeout values because of some security concern,
e.g., Section 10.5. However, the [Contrace Reply Timeout] value
SHOULD NOT be larger than 6 (seconds) and SHOULD NOT be lower than 3
(seconds).
8.2. HopLimit in Fixed Header
If a Contrace user does not specify the HopLimit value in a fixed
header for a Request message as the HopLimit, the HopLimit is set to
32. Note that a Contrace user specifies 0 as the HopLimit, it is an
invalid Request and discarded.
8.3. Access Control
A router MAY configure the valid or invalid networks to enable an
access control. The access control can be defined per name prefix,
such as "who can retrieve which name prefix". See Section 10.2.
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9. Diagnosis and Analysis
9.1. Number of Hops
A Contrace Request message is forwarded in a hop-by-hop manner and
each forwarding router appended its own Report block. We can then
verify the number of hops to reach the content forwarder or the
publisher.
9.2. Caching Router and Gateway Identification
It is possible to identify the caching routers or a gateway in the
path from the Contrace user to the content forwarder, while some
routers may hide their identifier (with all-zeros) in the Report
blocks (Section 10.1).
9.3. TTL or Hop Limit
By taking the HopLimit from the content forwarder and forwarding TTL
threshold over all hops, it is possible to discover the TTL or hop
limit required for the content forwarder to reach the Contrace user.
9.4. Time Delay
If the routers have synchronized clocks, it is possible to estimate
propagation and queuing delay from the differences between the
timestamps at successive hops. However, this delay includes control
processing overhead, so is not necessarily indicative of the delay
that data traffic would experience.
9.5. Path Stretch
By getting the path stretch "d / P", where "d" is the hop count of
the data and "P" is the hop count from the consumer to the publisher,
we can measure the improvement in path stretch in various cases, such
as different caching and routing algorithms. We can then facilitate
investigation of the performance of the protocol.
9.6. Cache Hit Probability
Contrace can show the number of received interests per cache or chunk
on a router. By this, Contrace measures the content popularity
(i.e., the number of accesses for each content/cache), and you can
investigate the routing/caching strategy in networks.
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10. Security Considerations
This section addresses some of the security considerations.
10.1. Policy-Based Information Provisioning for Request
Although Contrace gives excellent troubleshooting cues, some network
administrators or operators may not want to disclose everything about
their network to the public, or may wish to securely transmit private
information to specific members of their networks. Contrace provides
policy-based information provisioning allowing network administrators
to specify their response policy for each router.
The access policy regarding "who is allowed to retrieve" and/or "what
kind of information" can be defined for each router. For the former
access policy, routers having the specified content can examine the
signature enclosed in the Request message and decide whether they
should notify the content information in the Reply or not. If the
routers decide to not notify the content information, they reply the
Contrace Reply with the ReturnCode of ADMIN_PROHIB without appending
any Reply (sub-)block TLV. For the latter policy, the permission,
whether (1) All (all cache information is disclosed), (2) Partial
(cache information with the particular name prefix can (or cannot) be
disclosed), or (3) Deny (no cache information is disclosed), is
defined at routers.
On the other hand, we entail that each router does not disrupt
forwarding Contrace Request and Reply messages. When a Request
message is received, the router SHOULD insert Report block. Here,
according to the policy configuration, the Node Identifier field in
the Report block MAY be null (i.e., all-zeros), but the Request
Arrival Time field SHOULD NOT be null. At last, the router SHOULD
forward the Request message to the upstream router toward the content
forwarder if no fatal error occurs.
10.2. Filtering of Contrace Users Located in Invalid Networks
A router MAY support an access control mechanism to filter out
Requests from invalid Contrace users. For it, invalid networks (or
domains) could, for example, be configured via a list of allowed/
disallowed networks (as seen in Section 8.3). If a Request is
received from the disallowed network (according to the Node
Identifier in the Request block), the Request SHOULD NOT be processed
and the Reply with the ReturnCode of INFO_HIDDEN may be used to note
that. The router MAY, however, perform rate limited logging of such
events.
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10.3. Topology Discovery
Contrace can be used to discover actively-used topologies. If a
network topology is a secret, Contrace Requests may be restricted at
the border of the domain, using the ADMIN_PROHIB return code.
10.4. Characteristics of Content
Contrace can be used to discover what publishers are sending to what
kinds of contents. If this information is a secret, Contrace
Requests may be restricted at the border of the domain, using the
ADMIN_PROHIB return code.
10.5. Longer or Shorter Contrace Reply Timeout
Routers can configure the Contrace Reply Timeout (Section 8.1), which
is the allowable timeout value to keep the PIT entry. If routers
configure the longer timeout value, there may be an attractive attack
vector against PIT memory. Moreover, especially when the force
option (Section 5.2) is specified for the Contrace Request, a number
of Reply messages may come back and cause a response storm. (See
Section 10.7 for rate limiting to avoid the storm). In order to
avoid DoS attacks, routers may configure the shorter timeout value
than the user-configured Contrace timeout value. However, if it is
too short, the Request may be timed out and the Contrace user does
not receive the all Replies and only retrieves the partial path
information (i.e., information about part of the tree).
There may be the way to allow for incremental exploration (i.e., to
explore the part of the tree the previous operation did not explore),
whereas discussing such mechanism is out of scope of this document.
10.6. Limiting Request Rates
A router may limit Contrace Requests by ignoring some of the
consecutive messages. The router MAY randomly ignore the received
messages to minimize the processing overhead, i.e., to keep fairness
in processing requests, or prevent traffic amplification. No error
is returned. The rate limit is left to the router's implementation.
10.7. Limiting Reply Rates
Contrace supporting multipath forwarding may result in one Request
returning multiple Reply messages. In order to prevent abuse, the
routers in the traced path MAY need to rate-limit the Replies. No
error is returned. The rate limit function is left to the router's
implementation.
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10.8. Adjacency Verification
Contrace Request and Reply messages MUST be forwarded by adjacent
neighbor nodes or routers. Forwarding Contrace messages given from
non-adjacent neighbor nodes/routers MUST be prohibited. Such invalid
messages SHOULD be silently discarded. Note that defining the secure
way to verify the adjacency cannot rely on the way specified in CCNx
message format or semantics. An adjacency verification mechanism and
the corresponding TLV for adjacency verification using hop-by-hop TLV
header will be defined in a separate document.
11. Acknowledgements
The authors would like to thank Spyridon Mastorakis, Ilya Moiseenko,
and David Oran for their valuable comments and suggestions on this
document.
12. References
12.1. Normative References
[1] Mosko, M., Solis, I., and C. Wood, "CCNx Messages in TLV
Format", draft-irtf-icnrg-ccnxmessages-04 (work in
progress), March 2017.
[2] Bradner, S., "Key words for use in RFCs to indicate
requirement levels", RFC 2119, March 1997.
[3] Deering, S. and R. Hinden, "Internet Protocol, Version 6
(IPv6) Specification", RFC 2460, December 1998.
12.2. Informative References
[4] Asaeda, H., Matsuzono, K., and T. Turletti, "Contrace: A
Tool for Measuring and Tracing Content-Centric Networks",
IEEE Communications Magazine, Vol.53, No.3, pp.182-188,
March 2015.
[5] Malkin, G., "Traceroute Using an IP Option", RFC 1393,
January 1993.
[6] Asaeda, H., Mayer, K., and W. Lee, "Mtrace Version 2:
Traceroute Facility for IP Multicast", draft-ietf-mboned-
mtrace-v2-17 (work in progress), March 2017.
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Appendix A. Contrace Command and Options
The contrace command enables the Contrace user to investigate the
routing path based on the name prefix of the content (e.g.,
ccnx:/news/today), device name, and function (or application) name.
The name prefix, device name, and function name (or application name)
are mandatory but exclusive options; that is, only one of them should
be used with the contrace command at once.
The usage of contrace command is as follows:
Usage: contrace [-p] [-g] [-f] [-n] [-o] [-r hop_count] [-s
hop_count] [-w wait_time] name_prefix; or,
Usage: contrace [-r hop_count] [-s hop_count] [-w wait_time]
device_name | function_name (or application_name)
name_prefix
Name prefix of the content (e.g., ccnx:/news/today) the Contrace
user wants to trace. If the Contrace user specifies only a scheme
name, e.g., "ccnx:/", s/he must specify "-g" option (i.e.,
contrace -g ccnx:/). In that case, the Contrace user discovers
the router having the FIB of the specified scheme name and the RTT
between Contrace user and the router. The -p option allows a
partial match for the name prefix; otherwise, an exact match is
required.
device_name
Device name (e.g., ccnx:/%device/server-A, ccnx:/%device/sensor-
123) the Contrace user wants to trace. Here, we assume the
contrace command with the "%device" prefix indicates the trace
request for specified device/server/node, but defining the syntax
of device name specification is [TBD].
function_name (or application_name)
Function name (e.g., ccnx:/%function/firewall,
ccnx:/%function/transcoding/mpeg2-h.264) or application name
(e.g., ccnx:/%application/mplayer) the Contrace user wants to
trace. Here, we assume the contrace command with the "%function"
or "%application" prefix indicates the trace request for specified
function or application, but defining the syntax of function or
application name specification is [TBD].
g option
This option enables to discover a gateway that supports specified
scheme name and has multiple FIBs. When a Contrace user specifies
only a scheme name, e.g., "ccnx:/", this option must be specified
and other content name prefix is ignored.
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f option
This option enables to ignore the forwarding strategy and send
Contrace Requests to multiple upstream routers simultaneously.
The Contrace user could then trace the all potential forwarding
paths.
n option
This option can be specified if a Contrace user only needs the
routing path information to the specified content/cache and RTT
between Contrace user and content forwarder (i.e., cache
information is not given).
o option
This option enables to trace the path to the content publisher.
If this option is specified, each router along the path to the
publisher only forwards the Request message; it inserts each
Report block but does not send Reply even if it caches the
specified content. The publisher (who has the complete set of
content and is not a caching router) replies the Reply message.
Specifying only a scheme name is not allowed with this option.
r option
Number of traced routers. If the Contrace user specifies this
option, only the specified number of hops from the Contrace user
trace the Request; each router inserts its own Report block and
forwards the Request message to the upstream router(s), and the
last router stops the trace and sends the Reply message back to
the Contrace user. This value is set in the "HopLimit" field
located in the fixed header of the Request. For example, when the
Contrace user invokes the Contrace command with this option such
as "-r 3", only three routers along the path examine their path
and cache information. If there is a caching router within the
hop count along the path, the caching router sends back the Reply
message and terminates the trace request. If the last router does
not have the corresponding cache, it replies the Reply message
with NO_INFO return code (described in Section 3.1) with no Reply
block TLV inserted. The Request messages are terminated at
publishers; therefore, although the maximum value for this option
a Contrace user can specify is 255, the Request messages should be
in general reached at the publisher within significantly lower
than 255 hops.
s option
Number of skipped routers. If the Contrace user specifies this
option, the number of hops from the Contrace user simply forward
the Contrace Request messages without adding its own Report block
and without replying the Request, and the next upstream router
starts the trace. This value is set in the "SkipHopCount" field
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located in the Request block TLV. For example, when the Contrace
user invokes the Contrace command with this option such as "-s 3",
the three upstream routers along the path only forwards the
Request message, but does not append their Report blocks in the
hop-by-hop headers and does not send the Reply messages even
though they have the corresponding cache. The Request messages
are terminated at publishers; therefore, although the maximum
value for this option a Contrace user can specify is 255, if the
Request messages reaches the publisher, the publisher silently
discards the Request message and the request will be timed out.
w option
This option defines the Contrace timeout value (in seconds) that
the Contrace user will wait for the Reply. After the timeout, the
Contrace user terminates the Request and silently discards the
Reply message even if s/he receives the Reply. Note that routers
along the path can configure the Contrace Reply Timeout
Section 8.1, which is the allowable timeout value to keep the PIT
entry. In order to avoid DoS attacks Section 10, routers MAY
configure the shorter timeout value than the user-configured
Contrace timeout value. If it is shorter, the Request may be
timed out and the Contrace user may not receive the Reply as
expected.
Authors' Addresses
Hitoshi Asaeda
National Institute of Information and Communications Technology
4-2-1 Nukui-Kitamachi
Koganei, Tokyo 184-8795
Japan
Email: asaeda@nict.go.jp
Xun Shao
National Institute of Information and Communications Technology
4-2-1 Nukui-Kitamachi
Koganei, Tokyo 184-8795
Japan
Email: x-shao@nict.go.jp
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Thierry Turletti
Inria
2004 Route des Lucioles
Sophia Antipolis 06902
France
Email: thierry.turletti@inria.fr
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